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In this study, a non-linear sliding mode control (NLSMC) and new switching dynamics control strategy have been proposed for a unified power quality conditioner (UPQC) to improve the power quality problem in power system distribution network. The proposed non-linear sliding surface reflects the controlling action of the DC-link capacitor voltage with a variation of the system's damping ratio and permits the DC-link voltage to obtain a low overshoot and small settling time. This NLSMC technique combines with a novel synchronous-reference frame (SRF) control technique for generation of a rapid and stable reference signal for both shunt and series converters. A new switching dynamics control strategy has been designed for the voltage source converters of UPQC and this design helps in the reduction of band violation of the hysteresis band as well as improvement in the tracking behaviour of UPQC during grid perturbations. Consequently, NLSMC-SRF technique along with new switching strategy in UPQC provides an effective compensator for voltage/current harmonics, sag/swell, voltage unbalance and interruptions. The proposed control strategy of UPQC is validated through MATLAB/SIMULINK, followed by the experimental system using real-time hardware-in-the-loop. Adequate results are reported after a comparative assessment with the conventional proportional-integral and hysteresis controller.

This study proposes a command generator tracker-based direct adaptive control technique (CGT-DAC) in a three-phase three-wire unified power quality conditioner (UPQC). This proposed CGT-DAC improves the PQ issues such as current and voltage harmonics, sag/swell and voltage unbalance in the power system distribution network. CGT is a model reference control law for a linear time-invariant system with known coefficients and is formulated for the generation of reference signals for both shunt and series inverter. Furthermore, CGT can adaptively regulate the DC-link capacitor voltage without utilising additional controller. Moreover, DAC is designed to track a linear reference model to reduce the tracking error between model reference output and measured signal to be controlled. Therefore, the proposed CGT-DAC approach provides more robustness, flexibility and adaptability in all operating conditions of the power system over a conventional proportional-integral (PI) controller. This proposed control strategy of UPQC is validated through MATLAB/SIMULINK followed by the experimental system of realtime-hardware-in the loop-based OPAL-RT system and adequate results are reported after a comparative assessment with the conventional PI-controller.

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